International Journal of Minerals, Metallurgy and Materials

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Couple analyzing the acoustic emission characters from hard composite rock fracture

2004, 11(2): 97-100.

中文摘要(240) PDF(10) SpringerLink

摘要:
Rock mass is fractured media. Its fracture is a nonlinear process. The accumulation of acoustic emission (AE) is closely related to the degree of damage. The dynamics problem is simply described based on the non-equilibrium statistical theory of crack evolvement, trying to use the hybrid analysis of the statistical theory and scan electron microscopy (SEM), the characters of AE sig nals from rock damage in a mined-out area is synthetically analyzed and evaluated. These provide an evidence to reverse deduce and accurately infer the position of rock fracture for dynamical hazard control.

Mineral

A multi-objective decision-making method for the treatment scheme of landslide hazard

Quanmin Xie, Yuanyou Xia

2004, 11(2): 101-105.

中文摘要(271) PDF(13) SpringerLink

摘要:
The treatment engineering of landslide hazard is a complicated system engineering. The selecting treatment scheme is influenced by many factors such as technology, economics, environment, and risk. The decision-making of treatment schemes of landslide hazard is a problem of comprehensive judgment with multi-hierarchy and multi-objective. The traditional analysis hierarchy process needs identity test. The traditional analysis hierarchy process is improved by means of optimal transfer matrix here. An improved hierarchy decision-making model for the treatment of landslide hazard is set up. The judgment matrix obtained by the method can naturally meet the requirement of identity, so the identity test is not necessary. At last, the method is applied to the treatment decision-making of the dangerous rock mass at the Slate Mountain, and its application is discussed in detail.

Metallurgy

Metallurgical quality of CSP thin slabs

Deguang Zhou, Jie Fu, Yonglin Kang, Zhongbing Wang, Jing Li, Zhongbo Xu

2004, 11(2): 106-109.

中文摘要(246) PDF(10) SpringerLink

摘要:
The casting structure, chemical composition segregation, dendrite arm space, inclusiona and during the CSP (compact strip production) rolling process were investigated. The results show that the CSP thin slab has a feature of uniform fme grains, more columnar crystals, less central porosity and segregation etc. There is no great difference in macrostructure between the CSP thin slab and conventional slab; however, the fine dendrite structure of the CSP slab is more uniform. Moreover, the central porosity and segregation are obviously improved after the first pass; and the dendrite is bent along the rolling direction rather than broken into pieces.Small inclusions with the diameter less than 10 μm in the CSP slab are dominantly consisted of aluminates formed by Al deoxidation and Ca treatment and not floating out of the melt. The large size inclusions found in the continuous casting slab are very few.

Metallurgy

Feedback control strategy of longitudinal temperature and finished carbonization time for coke oven and its application

Fang Huo, Zhi Wen, Dong Chen, Yueling Shen, Yongqin Zhang, Xiaoming Zhi

2004, 11(2): 110-114.

中文摘要(290) PDF(15) SpringerLink

摘要:
Based on the detailed analysis of the third coke oven in BaoSteel, a feedback control strategy of longitudinal temperature and finished carbonization time of coke ovens was proposed and it was applied to the third coke oven in BaoSteel. As a result, the ratio of the instance that the absolute deviation of the longitudinal temperature is within ±7°C and the finished carbonization time within ± 10 min is more than 80%, having acquired the patent saving effect of an energy consumption lowered by 2.92%. At the same time, it can provide an example for the same coke ovens inside and outside the nation.

Metallurgy

Influence of operation parameters on flash smelting furnace based on CFD

Xinfeng Li, Shiheng Peng, Xiangli Han, Chi Mei, Tianyuan Xiao

2004, 11(2): 115-119.

中文摘要(432) PDF(54) SpringerLink

摘要:
The influence of three important operation parameters in Jinlong flash smelting furnace, including the distributing blast speed, the oxygen enrichment rate of process air and the ratio of central oxygen to overall oxygen (O_c/O_o), has been investigated using a virtual simulation system on copper flash smelting furnace. The core of this virtual simulation system is a numerical simulation of CFD (computational fluid dynamics), and this system incorporates coupling momentum transport, heat transport, mass transport,reaction kinetics between gas and particles and chemical reactions between gas and gas. A set of numerical predicted data were obtained. The CFD simulation shows that there is a sensitive zone of the distributing blast speed, and the dust content ascends when the speed exceeds 180 m·s^-1. Increasing the oxygen concentration of processing air benefits the efficient production of the flash smelting furnace.

Metallurgy

Analytical solutions to a compressible boundary layer problem with heat transfer

Liancun Zheng, Xinxin Zhang, Jicheng He

2004, 11(2): 120-122.

中文摘要(253) PDF(11) SpringerLink

摘要:
The problem of momentum and heat transfer in a compressible boundary layer behind a thin expansion wave was solved by the application of the similarity transformation and the shooting technique. Utilizing the analytical expression of a two-point boundary value problem for momentum transfer, the energy boundary layer solution was represented as a function of the dimensionless velocity, and as the parameters of the Prandtl number, the velocity ratio, and the temperature ratio.

Materials

Effects of electric pulse on microstructure of Al-Si alloy in liquid and solid states

Jingsong Wang, Qingguo Xue, Guowei Chang, Yong Tang, Jianzhong Wang, Daqiang Cang

2004, 11(2): 123-126.

中文摘要(272) PDF(10) SpringerLink

摘要:
In order to investigate the change in liquid microstructure of Al-Si alloy treated by electric pulse (EP), X-ray diffraction tests with liquid Al-Si alloy and ZL109 alloy treated or not by EP were carried out. The results show that the number of Al-Si atomic clusters decreases and that of Al-Al and Si-Si atomic clusters increases for the treated samples. The tests with ZL109 alloy indicate that a large amount of primary crystal Si appears in the solidified microstructure after treated by EP. It is found that EP canchange the microstructure of liquid metal by affecting the probability of electrons appearing in different atoms (Al and Si) in the liquid metal.The combining force of different atoms decreases relatively, and that of the same atoms increases, which is the main reason of reducing the atomic cluster with different atoms (Al-Si) and increasing the atomic cluster with the same atoms (Al-Al, Si-Si). The increasing of the atomic cluster with the same atom cluster resulted in the increasing of Si activity and the higher point of eutectics in the phase diagram. It makes a lot of primary silicon appeared in ZL109 alloy.

Materials

Galvanic corrosion behavior of die cast AZ91D magnesium alloy in chloride solution

Zhensong Tong, Wei Zhang, Jiuqing Li, Jin Gao, Jiquan He, Ji Zhou

2004, 11(2): 127-132.

中文摘要(299) PDF(11) SpringerLink

摘要:
The galvanic corrosion behavior of die cast AZ91D magnesium alloy coupled with H62 brass, 316L stainless steel, A3 steel and LY12 aluminum alloy of different areas in 3.5% NaCl solution was studied. The free corrosion potentials, galvanic potentials and currents of these galvanic couples were measured. The galvanic effects were determined by the mass loss and regression method using three points. The results show that: (1) In these four kinds of couples AZ91D acts as the anode, whose galvanic corrosion behavior is mainly controlled by the cathodic polarization; (2) The free corrosion potentials of these four kinds of couples change a liffle with time and cathodic/anodic area ratio (CAAR); (3) The galvanic potential of AZ91D/LY12 moves positively with the increase of time and CAAR; (4) The galvanic currents increase with CAAR, but there is difference in the current change between different couples; (5) The anodic dissolution rate of the magnesium alloy increases by 2-3 orders after being coupled with these four kinds of metals and the galvanic effects of these couples have such a relation as γ_H62>γ_316LS.S>γ_LY12>γ_A3.

Materials

Grain refinement of low carbon steel produced by CSP process

Xiangdong Huo, Delu Liu, Yuanli Wang, Nanjing Chen, Yonglin Kang, Jie Fu

2004, 11(2): 133-137.

中文摘要(251) PDF(18) SpringerLink

摘要:
In comparison with conventional production for hot strips, compact strip production (CSP) brings about some new microstructural phenomena. Investigations were carried out to clarify the grain refinement mechanism of low carbon steel strips produced by the EAF-CSP process. Samples, obtained from the same rolling stock during continuous rolling, were examined through SEM,TEM and XEDS. Thin slabs have a dominant columnar structure and the spacing of the secondary dendrite arms ranges from 90 to ~125 μm. The average grain sizes for the central area of the samples from the 1st to 6th pass are 41.6, 25.2, 21.4, 20.2, 13.1, 6.7 μm,respectively. Large number of nanometer oxide and sulfide have been found in the low carbon steel produced by the CSP process.The grain refinement mechanism can be summarized as follows: finer solidification structure of the thin slab; austenite recrystallization at higher temperature and stain accumulation at lower temperature caused by the great reduction of single rolling pass during continuous rolling; nano-scaled precipitates of sulfide and oxide which drag grain boundaries of austenite or ferrite to prevent the grain coarsening.

Materials

Verification of topological relationship in 2-D grain growth process by simulation

Chao Wang, Guoquan Liu, Ya Sun, Xiangge Qin

2004, 11(2): 138-140.

中文摘要(189) PDF(7) SpringerLink

摘要:
Behaviors of the quasi-steady state grain size distribution and the corresponding topological relationship were investigated using the Ports Monte Carlo method to simulate the normal grain growth process. The observed quasi-steady state grain size distribution can be well fit by the Weibull function rather than the Hillert distribution. It is also found that the grain size and average number of grain sides are not linearly related. The reason that the quasi-steady state grain size distribution deviates from the Hillert distribution may contribute to the nonlinearity of the relation of the average number of grain sides with the grain size. The results also exhibit the reasonability of the relationship deduced by Mullins between the grain size distribution and the average number of grain sides.

Materials

Influence of hydrogen content on the behavior of grain reflnement in hypereutectic aluminum-silicon alloy

Lina Hu, Xiufang Bian, Youfeng Duan

2004, 11(2): 141-146.

中文摘要(212) PDF(7) SpringerLink

摘要:
Dissolved hydrogen is harmful to mechanical properties of refined hypereutectic aluminum-silicon alloys. In the present work, by using a stepped-form mold and the hydrogen-detecting instrument HYSCAN Ⅱ, the relationship between the initial hydrogen content in the melt and the refinement effect on the casting of hypereutectic aluminum-silicon alloy was investigated. The experimental results show that the cooling rate, the hydrogen content and the grain refinement effect are three interactive factors. When the hydrogen content is above 0.20 mL/100 g and the cooling rate is lower than that in 50 mm-thick step, hydrogen dissolved in the alloy melt influences the grain refinement effect. With increasing the cooling rate, the critical hydrogen content increases too. It is expected that much hydrogen in the melt make the net interfacial energy larger than or equal to zero, resulting in the shielding of the particles AlP during solidification and that the critical gas content is closely related to the critical radius of embryo bubbles.

Materials

Corrosion behaviors of NdFeB magnets prepared by spark plasma sintering

Tao Li, Ming Yue, Aizhi Sun, Baoqin Qiu, Yaofu Xiao, Jiuxing Zhang

2004, 11(2): 147-150.

中文摘要(387) PDF(11) SpringerLink

摘要:
The spark plasma sintering (SPS) technique was introduced into the field of NdFeB preparation due to its own advantages.High property NdFeB magnets with fine grains were prepared by SPS method. The corrosion behaviors of SPS NdFeB were studied by electrochemical measurements and 92% RH hyther tests at 353 K. The results were compared with those of the traditional sintered NdFeB magnets. It shows that both the SPS NdFeB and the traditional sintered NdFeB have good corrosion resistance in alkaline environment due to surface passivation; while, the fine grain microstructure of SPS NdFeB results in a more homogeneous phase composition distribution and thus reduces the electrochemical inhomogenity between the ferromagnetic phase and the Nd-rich intergranular phase in the magnet. Therefore, the SPS NdFeB exhibits better corrosion resistance than the traditional sintered NdFeB in neutral and weak acidic environment.

Materials

XPS study of the corrosion resisting composite alloying layer obtained by double glow plasma with the brush plating Ni interlayer

Jiang Xu, Xishan Xie, Zhong Xu, Wenjin Liu

2004, 11(2): 151-156.

中文摘要(225) PDF(7) SpringerLink

摘要:
The Ni-Cr-Mo-Cu multi-element surface alloying with the electric brush plating Ni interlayer on the low carbon steel substrate has been investigated. By the electrochemical method in 3.5% (mass fraction) NaCl solution, the corrosion resistance of the composite alloying layer and single alloying layer is determined. The experimental results show that the corrosion resistance of the composite alloying layer is obviously better than that of the single alloying layer. The structure and composition of passive films formed on the two kinds of alloyed layers after electrochemical tests in 3.5% NaCl solution have been studied using X-ray photoelectron spectroscopy (XPS). It is concluded that the double glow plasma surface alloying of low carbon steel with the electric brush plating Ni interlayer is an appropriate technique to enhance the corrosion resistance compared with the single double glow surface alloying.

Materials

Enhancement of heat radiative characteristics of coatings by ultra-attenuation

Dehong Xia, Yonghong Wu

2004, 11(2): 157-160.

中文摘要(247) PDF(7) SpringerLink

摘要:
The absorption process of radiative heat in its transmission medium and the effect of ultra-attenuation on the radiative characteristics are analyzed in detail. A method of ultra-attenuation to enhance the radiative characteristics of the medium is proposed. It is proved that decreasing the particle size of coatings can increase the transmission depth of radiative heat and get higher emissivity and absorptivity both theoretically and practically. Ultra-attenuation and nanocrystallization will bring a brilliant prospect to the development of radiative coatings.

Materials

Liquid structure of pure iron by X-ray diffraction

Jun Luo, Qijie Zhai, Pei Zhao, Xubo Qin

2004, 11(2): 161-164.

中文摘要(417) PDF(21) SpringerLink

摘要:
The liquid structure of pure iron at 1540, 1560 and 1580℃ was studied by X-ray diffraction. The results show that near the melting point there is a medium-range order structure that fades away with the increasing temperature. The average nearest distance of atoms is almost independent of the melts temperature, but the average coordination number, the atom cluster size and the atom number in an atom cluster all decrease with the increasing temperature of the melt. Near the melting point there area lot of atom clusters in the pure iron melt. The atom cluster of pure iron has the body-centered cubic lattices, which are kept from the solid state. And the body-centered cubic lattices connect into network by occupying a same edge. The atoms in the surrounding of the atom clusters are arranged disorderly.

Materials

Interfacial mechanical property of steel-mushy Al-20Sn bonding

Peng Zhang, Yunhui Du, Hanwu Liu, Daben Zeng, Jianzhong Cui, Limin Ba

2004, 11(2): 165-168.

中文摘要(259) PDF(7) SpringerLink

摘要:
The bonding of a steel plate to Al-20Sn slurry was conducted using the casting rolling technique. The surface of the steel plate was defatted, descaled, immersed (in K₂ZrF₆ flux aqueous solution) and stoved. Al-20Sn slurry was prepared using the electromagnetic mechanical stirring method. The interfacial mechanical property of the bonding plate was researched to determine the relationship between the diffusion time and the interfacial shear strength. In order to identify the mechanism of bonding, the interfacial structure of the bonding plate was studied. The results show that at a preheat temperature of the steel plate of 505℃ and a solid fraction of Al-20Sn slurry of 35%, the relationship between the interfacial shear strength S and the diffusion time t is S=28.8+4.3t-0.134t² +0.0011t³. When the diffusion time is 22 s, the largest interfacial shear strength is 70.3 MPa, and the corresponding interface is a new one which is made up of Fe-Al compound and Fe-Al solid solution alternatively and in a right proportion.In this interfacial structure, the interfacial embrittlement does not happen and Fe-Al compound can play its role in strong combination adequately.

Materials

Fabrication of directional solidification components of nickel-base superalloys by laser metal forming

Liping Feng, Weidong Huang, Darong Chen, Xin Lin, Haiou Yang

2004, 11(2): 169-172.

中文摘要(275) PDF(12) SpringerLink

摘要:
Straight plates, hollow columns, ear-like blade tips, twist plates with directional solidification microstructure made of Rene 95 superalloys were successfully fabricated on Nickel-base superalloy and DD3 substrates, respectively. The processing conditions for production of the parts with corresponding shapes were obtained. The fabrication precision was high and the components were compact. The solidification microstructure of the parts was analyzed by optical microscopy. The results show that the solidification microstructure is composed of columnar dendrites, by epitaxial growth onto the directional solidification substrates. The crystallography orientation of the parts was parallel to that of the substrates. The primary arm spacing was about 10 μm, which is in the range of superfine dendrites, and the secondary arm was small or even degenerated. It is concluded that the laser metal forming technique provides a method to manufacture directional solidification components.

Materials

Analysis of the thermal profile of work rolls in the hot strip rolling process

Xuanli Zhang, Jie Zhang, Xiaoyan Li, Haixia Li, Gangcheng Wei

2004, 11(2): 173-177.

中文摘要(302) PDF(148) SpringerLink

摘要:
A 2-dimension axisymmetric model was developed by the finite-difference method, which can be used to predict the transient temperature field and thermal profile of work rolls in the hot strip rolling process. To demonstrate the accuracy and reliability of the solution developed, the calculation results were compared with the production data of a 1700 mm hot strip rolling mill and good agreement was found between them. The effect of strip width and roll shifting on the thermal expansion of the work rolls was studied.It is found that the strip width has marked effect on the efficient thermal crown. Initially, when the rolling strip changes from narrow to wide, a bigger efficient thermal crown can be quickly achieved; afterwards, when the rolling strip changes from wide to narrow,not only the influence of uneven wear can be reduced but also the excessive efficient thermal crown can be avoided. It is also found that the work roll shifting has a determinate but not obvious effect on the reduction of the efficient thermal crown, and will make the strip shape unstable without being used properly.

Materials

Deforming analysis of sheet metal based on stereo vision and coordinate grid

Hongqin Wei, Dehong Yu, Xueyu Ruan, Youqing Wang

2004, 11(2): 178-182.

中文摘要(235) PDF(6) SpringerLink

摘要:
A new approach based on stereo vision technology is introduced to analyze sheet metal deformation. By measuring the deformed circle grids that are printed on the sheet surface before forming, the strain distribution of the workpiece is obtained. The measurement and analysis results can be used to verify numerical simulation results and guide production. To get good accuracy,some new techniques are employed: camera calibration based on genetic algorithm, feature abstraction based on self-adaptive technology, image matching based on structure feature and camera modeling pre-constrains, and parameter calculation based on curve and surface optimization. The experimental values show that the approach proposed is rational and practical, which can provide better measurement accuracy with less time than the conventional method.

Automation

An input signal used in process identification - chaos sequence

Geng Zhao, Deling Zheng, Shaojun Huang

2004, 11(2): 183-186.

中文摘要(231) PDF(7) SpringerLink

摘要:
The sequences which consist of any segment of a chaos sequence are called as C-sequences. These sequences could be used as a kind of input signals to replace M-sequences in the process identification. This substitution is theoretically proved to be feasible. Inverse C-sequences are created in a way similar to inverse M-sequences to solve the problem that C-sequences have nonideal balance property, that is, the numbers of ‘0’ and ‘1’ are unequal. Besides its good pseudo-random property, the sequences have other advantages such as easy to generate, varieties of the segment and adjustable cycle time.

Communication

Formation mechanism of Ti₅Si₃ powder by mechanical alloying

Pengchao Kang, Zhongda Yin, Yue Jiang, Mingwei Li

2004, 11(2): 187-189.

中文摘要(291) PDF(7) SpringerLink

摘要:
The formation mechanism of stoichiometry Ti₅Si₃ by mechanical alloying (MA) from elemental powders has been investigated. The results of XRD and SEM analyses of the powder show that Ti₅Si₃ can be synthesized by MA in a planetary mill with two different formation mechanisms. Ti₅Si₃ was formed gradually with the mechanical collusion reaction (MCR) mechanism under a lower impact energy, and the Ti₅Si₃ was formed abruptly with the self-propagating high-temperature synthesis (SHS) formation mechanism under a higher impact energy.

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